Zakynthos lies in the eastern part of the Ionian sea, around 20 kilometres (12 miles) west of the Greek (Peloponnese) mainland. Island of Kefalonia lies 15 kilometres (9 miles) on the north. It is the southernmost of the main group of the Ionian islands (not counting distant Kythira).
The western half of the island is a mountainous plateau and the southwest coast consists mostly of steep cliffs. The eastern half is a densely populated fertile plain with long sandy beaches, interrupted with several isolated hills, notably Bochali which overlooks the city and the peninsula of Vasilikos in the northeast. The peninsulas of Vassilikos on north and Marathia on south enclose the wide and shallow bay of Laganas on the southeast part of the island. The capital, which has the same name as the prefecture, is the town of Zakynthos. It lies on the eastern part of the northern coast.